Strategy of paramyxovirusto attenuate cytopathicity

包括猿猴病毒5（SV5）在内的副粘病毒通过病毒包膜糖蛋白HN和F之间的相互作用介导膜融合，其中HN蛋白促进F蛋白的融合诱导功能。我在这里报告SV5 HN蛋白的茎区参与与F蛋白的相互作用，与其他副粘病毒相同。此外，我首次报道了F蛋白的四个离散结构域参与与FIN蛋白的相互作用。另一方面，正如之前发表的那样，与原型WR菌株相比，SV5 T1菌株诱导细胞-细胞融合的能力降低，因此对病毒感染的细胞带来的细胞病变最小。为探讨T1病毒减毒的分子机制，采用空斑克隆技术从T1病毒中获得高融合性变异体。该变异在FIN蛋白中具有L182R、K45 IT和V536M三个突变，而在F蛋白中没有突变。值得注意的是，L182R突变被证明提高了HN蛋白的促进融合功能，182位亮氨酸突变为除Ala以外的其他氨基酸也促进了HN蛋白的促进融合功能。然而，将HN和/或F蛋白替换为Ti对应蛋白的重组WR病毒均具有融合性，这表明其他T1病毒蛋白如M蛋白可能参与了T1 FIN蛋白的融合抑制功能。由于T1病毒可以进行多步复制，包膜和细胞膜之间的融合似乎是正常进行的。因此，我们假设T1 FIN蛋白可能通过向细胞内分子（如肌动蛋白或血管蛋白）转导信号来抑制细胞-细胞融合，而L182R突变或与WR M蛋白的结合可能以某种方式取消这种信号转导的抑制。

Paramyxoviruses including simian virus 5(SV5)mediate membrane fusion through an interaction between viral envelope glycoproteins HN and F, in which the HN protein promotes fusion-inducing function of the F protein. I report here that the stalk region of SV5 HN protein is involved in the interaction with the F protein the same as those of other paramyxoviruses. Furthermore, I report for the first time that four discrete domains of the F proteins participate in the interaction with the FIN protein. As published previously, on the other hand, the T1 strain of SV5 displays reduced ability to induce cell-cell fusion and thus brings minimal cytopathicity to the virus-infected cells as compared to the prototype WR strain. To investigate the molecular mechanism of the attenuated cytopathicity of T1 virus, highly fusogenic variant was obtained from T1 virus by plaque cloning. This variant possessed three mutations L182R, K45 IT, and V536M in the FIN protein, with no mutation in the F protein. Notably, L182R mutation proved to raise the fusion-promoting function of the HN protein and that mutation of leucine at position 182 to other amino acids other than Ala also facilitates the fusion-promoting function of the HN protein. However, either of the recombinant WR viruses whose HN and/or F proteins had been replaced with the Ti counterparts were fusogenic, indicating that other T1 virus proteins such as M protein might contribute to the fusion-inhibiting function of the T1 FIN protein. Since T1 virus could perform multiple-step replication, the fusion between envelope and cell membrane seems to take place normally. We thus hypothesize that T1 FIN protein may suppresses cell-cell fusion by transducing a signal to the intracellular molecules such as actin or vinculin that the L182R mutation or combination with WR M protein may somehow cancel this suppression of signal transduction.